The invention relates to a process for the preparation of higher carboxylic acids.
It is known that it is possible to obtain carboxylic acids from petrochemical raw materials by the direct oxidation of olefins with nitric acid. The method of preparation, however, has the disadvantage that the reaction is not easily controlled since during the process isomerizations may take place in the olefin and therefore carboxylic acids of different chain lengths result. In addition the mixtures of carboxylic acids obtained are considerably contaminated with nitrogen containing compounds, especially nitro-compounds, and moreover, are only obtained in moderate yields. Better results are attained when the olefins are first converted into compounds which contain polar groups attached to two adjacent carbon atoms, for example, hydroxy, ether, ester and/or epoxy groups. Such compounds may be converted into carboxylic acids with higher yields in the presence of the usual oxidation catalysts. Transition metals or their compounds, such as salts or oxides, especially vanadium and vanadium compounds, serve as oxidation catalysts. It is detrimental to employ such a method because the presence of the catalyst considerably impedes the preparation and purification of the products, while giving rise to undesirable consecutive reactions. The separation of the catalyst itself necessitates complicated separation methods, for example the insertion of special exchange resins stable to oxidation, and when such resins are used it is also necessary to conduct the reaction at specific pH values.